Get out of "orange selection" mode
The reason you can't select other objects is because you are in Edit Mode.
The reason for the orange outlines is likely due to having entered edit mode (&#8633; Tab) while all objects were selected (A):



While in edit mode, you can edit the mesh of the Active object, but cannot move any other objects. To select a different active object for editing, you'll have to first toggle back to Object Mode (&#8633; Tab) before clicking an object with  RMB.

Also see the blender manual.